The top U.S. military commander in South Korea is urging North Korea to lower tensions on the divided peninsula, in the wake of reports that Pyongyang is preparing to test a long-range ballistic missile.

General Walter Sharp says the United States and South Korea are keeping a close eye on the communist regime, and are prepared for what he called "any contingency."

Media reports in South Korea say intelligence officials in both nations have recently observed a train carrying what is believed to be Taepodong-Two missile.

Sharp is calling on North Korea to stop its recent "provocations," such as ending all previous military and political accords with Seoul.

Observers believe Pyongyang is raising tensions on the peninsula to attract the attention of new U.S. President Barack Obama.

A U.S. State Department spokesman told reporters in Washington Tuesday that any North Korean ballistic missile test would be a provocation.

North Korea successfully tested a Taepodong-One missile in over Japan in 1998. A test of its Taepodong-Two missile failed in 2006.

Washington and Seoul are engaged in six-nation negotiations along with Russia, China and Japan, as well as North Korea aimed at ending North Korea's nuclear programs. The talks are in a stalemate over ways to verify North Korea's declared nuclear activities.

Relations between North and South Korea have worsened since conservative President Lee Myung-bak took office last year, vowing to take a harder stance against the North over the nuclear disarmament issue.